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09-29-2015, 12:36 PM   #1
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Unwanted AF triggering in middle of interval timer

I was taking a series of photos for a timelapse of last Sunday night's lunar eclipse. The autofocus engaged in the middle of the series, racking all the way in and out, forcing me to cancel the timelapse. I'm trying to figure out if this was a one time glitch or if there's some setting on my K5 I need to correct. Notes follow.

1) Camera was in Manual exposure. I was using 1/4 second shutter speed. The interval timer was set to 15 seconds between shots.

2) AF is configured for back button. Shutter half press does nothing but wake up the camera if it's gone into power save mode.

3) I was definitely not touching the camera when the AF engaged.

4) Focus mode switch started in MF while I manually focused, then flipped to AF.S to lock the focus ring from moving during the timelapse.

5) I periodically shined a light into the lens to check for dew. The AF fired shortly after one of these checks. I'm not sure if that's related or just coincidence.

6) I did 3 timelapses that night. The random AF only happened for the first one. The next 2 worked fine.

09-29-2015, 01:30 PM   #2
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Normal behavior. Keep it on MF.
09-29-2015, 02:45 PM   #3
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QuoteOriginally posted by vonBaloney Quote
Normal behavior. Keep it on MF.
What he said. The general rule is to turn AF off unless you want unintended results or have significant control over what happens withing range of the potential AF points.


Steve
09-29-2015, 04:12 PM   #4
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Really, normal behavior? Time lapses try to refocus AF with every image? I took 300 images and I only heard the AF motor once.

Leaving the body switch in MF for astrophotography time lapses can be bad: it disengages the screw drive, which then allows focus creep as the lens is aimed up.

09-29-2015, 04:37 PM   #5
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AF.S will try to focus each shot individually.

You may get lucky and the lens stays still, but the auto focus sensor checks each shot and adjusts if necessary.

If you are worried about focus creep in manual focus mode, tape the focus ring in place.

this is not related to it being a time lapse
09-29-2015, 04:43 PM   #6
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QuoteOriginally posted by DeadJohn Quote
Really, normal behavior? Time lapses try to refocus AF with every image? I took 300 images and I only heard the AF motor once.
Yep, try it in the daylight and stand around in front of the lens at different distances -- it will refocus. You can probably imagine a scenario where this is desired behavior.

So for fixed focus, leave on MF. If focus drift is a worry, use a rubber band across focus ring to create extra friction. Or a bit a gaffer tape, but it makes it a little harder not to move focus as you put the tape down (apply tape beforehand and leave it as a little flap hanging up so once you get your focus you just press it straight down).
09-29-2015, 07:10 PM   #7
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QuoteOriginally posted by DeadJohn Quote
Leaving the body switch in MF for astrophotography time lapses can be bad: it disengages the screw drive, which then allows focus creep as the lens is aimed up.
Tape or wedge the lens. That is the traditional approach. With my Sigma 17-70 (c) I disengage AF on the body and leave the lens switch in the on position. The motor resistance enough to keep the focus ring in place. Zoom creep is another matter


Steve
09-29-2015, 07:38 PM   #8
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Thanks for the quick answers. Yeah, I just tested and confirmed that AF tries to activate every interval. I've done a few dozen astro time lapses but I usually use an MF lens so never had to worry about unwanted AF.

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